The present invention relates to a noncontact sensor for longitudinal travel, and more particularly, to brake pedal position sensing integral to a master cylinder for an automotive hydraulic braking system.
Automobiles have long incorporated hydraulic wheel braking systems that rely upon a master cylinder to supply hydraulic pressure to disk brake calipers or drum brake actuators in response to brake pedal pressure. The driver adjusts the amount of pedal pressure to accommodate variations in stopping performance and driving conditions.
More recently, improvements to hydraulic braking systems have enhanced performance and safety. For instance, Electro-Hydraulic Braking (EHB) systems automatically adjust a commanded degree of braking to accommodate variations in the braking system and driving conditions. The brake pedal becomes an input rather than a direct control to the EHB system. Consequently, determining the amount of braking intended by the driver becomes important to correct operation of the braking system and for providing feedback to the driver. Some EHB systems use a number of devices for determining the amount of braking intended by the driver. These devices include a pressure sensor or transducer exposed to the hydraulic fluid that goes to the wheel brakes. However, the sensed pressure may not directly correspond to the amount of pressure applied to the brake pedal for small travel events due to friction in the braking system or other variations.
It is known to use a Hall Effect sensor to sense a pressure imbalance between two braking circuits. A magnet within the hydraulic portion of the master cylinder is physically separated from the Hall Effect transducer that senses the position of the magnet. However, the Hall Effect transducer has a limited range of less than an inch for sensing the position of the magnet, and thus was used as a switch rather than for sensing a range of pressures.
It is known to sense brake pedal position directly, rather than hydraulic pressure for short travel events. In particular, contact transducers, such as resistive strip potentiometers, are mechanically connected to the brake pedal linkages. However, these contact transducers suffer from variations in signal output due to physical wear. Moreover, integration of noncontact sensors is complicated, first by the geometry of brake pedal linkages for different vehicles; second, the adjustment of a brake pedal to accord different users of the same vehicle type; and third by nonstandard brake pedals for the disabled (e.g., hand brake). Moreover, these portions of the braking system are often designed by different vendors, thereby further complicating the design effort.
Consequently, a significant need exists for brake pedal position sensing that can be readily integrated into a wide variety of vehicle types and that is less subject to performance variation.
The present invention addresses these and other problems in the prior art by providing a noncontact position sensor integral to a master cylinder for an automotive hydraulic braking system.
Thus, reliable brake pedal position information is readily provided without regard to the geometry and placement of the brake pedal input, thereby decreasing the complexity of integration into each type of automobile. An advantage of the present invention is that reliable performance of brake position sensing is provided by the use of non-contact sensors that are less subject to wear and performance variations, thereby providing a more reliable performance over a longer time than known sensors.
In one aspect of the invention, a hydraulic braking master cylinder includes a sensor for determining travel. In particular, the sensor includes a dual Hall Effect transducer arrangement to sense a magnet coupled to a piston. The dual transducers increase the length of travel that may be sensed.
In another aspect of the invention, the sensor further includes circuitry for determining the travel position based on the outputs from the dual transducers. In particular, based on the voltage levels from each transducer, the circuitry determines a region of operation and uses a linear approximation based on one of the two transducers appropriate for that region. Thereby, a complicated computation or lookup of the position based on a nonlinear representation of the transducer signals is avoided.
In yet another aspect of the invention, a sensor for determining travel senses a magnetic field of a magnet coupled to a member by spacing a first and second Hall Effect transducer spaced along a direction of travel of the member. A linear approximation is defined for each linear portion of output signals from each respective Hall Effect transducer. The linear approximation is a function of travel, sensor gain, and an offset. Determining travel based on the output signals is achieved by determining a region of operation by solving each linear approximation function with the related output signal and selecting a linear approximation with a lower magnitude. A signal representing travel is produced by solving the selected linear approximation for travel.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.